1. Field of the Invention
The present invention relates to methods for making molded glass and ceramic articles. More particularly, the present invention relates to an improved sol-gel method for making molded glass and ceramic articles using aqueous fluorine to initiate a gel reaction.
2. Description of the Related Art
One of the established methods of making glass and ceramic articles is known as the "sol-gel" method. When making articles using this process, a base material in the form of fine particles is mixed with water and various stabilizing ingredients to form a stable dispersion or "sol." To this sol, an "initiator" is added to destabilize the dispersion, causing the fine particles to bond together and form a "gel." One common initiator is aqueous fluorine, which is typically added as hydrofluoric acid or ammonium hydrofluoride. Upon adding the initiator, the dispersion may be transferred to a mold. After the dispersion gels, the gel is removed from the mold, dried, and fired.
One problem inherent in the sol-gel method arises from adding the initiator. If the initiator is added directly to the sol, problems may arise in controlling the gelling process. For example, the sol may gel before it can be transferred to the mold. One technique to solving this problem when using fluorine as the initiator is disclosed in U.S. Pat. No. 4,840,653, issued to Rabinovich. This patent discloses reacting a silicon-containing organic chemical with water and hydrofluoric acid to create a fluorinated form of finely divided silica. A small amount of this material is then added to a dispersion of nonfluorinated fine silica to initiate the gelling reaction in a timely and controlled fashion.